Familial opposable triphalangeal thumbs duplication: A rare birth malformation where the thumb has three bones instead of the normal two which gives it a fingerlike appearance. An extra toe is also present. 

J Med Genet. 1985 Feb;22(1):78-80.

Familial opposable triphalangeal thumbs associated with duplication of the big toes.

Merlob P, Grunebaum M, Reisner SH.

Abstract

A rare association of triphalangeal thumbs and duplication of the big toes is described. The family pedigree confirms autosomal dominant inheritance with marked penetrance. A systematic approach to the diagnosis of this anomaly is presented. The distinction between the two types of triphalangeal thumb, true (opposable) and finger-like (non-opposable), is emphasised.